function code_draw () {
    var canvas_width = $('#canvas').width();
    var canvas_height = $('#canvas').height();
    var canvas = document.getElementById("canvas"); //获取到canvas的对象，演员
    if (!canvas) {
        return;
    }
    var context = canvas.getContext("2d"); //获取到canvas画图的环境，演员表演的舞台
    canvas.width = canvas_width;
    canvas.height = canvas_height;
    var sCode = "A,B,C,E,F,G,H,J,K,L,M,N,P,Q,R,S,T,W,X,Y,Z,1,2,3,4,5,6,7,8,9,0"; //取值范围
    var aCode = sCode.split(",");
    var aLength = aCode.length; //获取到数组的长度
    var value = [];
    for (var i = 0; i <= 3; i++) {
        var j = Math.floor(Math.random() * aLength); //获取到随机的索引值
        var deg = Math.random() * 30 * Math.PI / 180; //产生0~30之间的随机弧度
        var txt = aCode[j]; //得到随机的一个内容
        value[i] = txt.toLowerCase();
        var x = 10 + i * 20; //文字在canvas上的x坐标
        var y = 20 + Math.random() * 8; //文字在canvas上的y坐标
        context.font = "bold 23px 微软雅黑";

        context.translate(x, y);
        context.rotate(deg);

        context.fillStyle = code_randomColor();
        context.fillText(txt, 0, 0);

        context.rotate(-deg);
        context.translate(-x, -y);
    }
    // 将生成的值以属性的方法添加到元素
    value = value.join("");
    $('#canvas').attr('data-code', value)
    //验证码上显示线条
    for (var i = 0; i <= 5; i++) {
        context.strokeStyle = code_randomColor();
        context.beginPath();
        context.moveTo(Math.random() * canvas_width, Math.random() * canvas_height);
        context.lineTo(Math.random() * canvas_width, Math.random() * canvas_height);
        context.stroke();
    }
    //验证码上显示小点
    for (var i = 0; i <= 30; i++) {
        context.strokeStyle = code_randomColor();
        context.beginPath();
        var x = Math.random() * canvas_width;
        var y = Math.random() * canvas_height;
        context.moveTo(x, y);
        context.lineTo(x + 1, y + 1);
        context.stroke();
    }
}

function code_randomColor () { //得到随机的颜色值
    var r = Math.floor(Math.random() * 256);
    var g = Math.floor(Math.random() * 256);
    var b = Math.floor(Math.random() * 256);
    return "rgb(" + r + "," + g + "," + b + ")";
}
